As is known, microfluidic systems are being used in an increasing number of applications, including biological applications. In such biological applications, it is often a necessary function to “hold” a cell or other biological object (e.g. ova, embryo, etc.) at a known physical location within the microfluidic device in order to perform some type of manipulation of that object. Because of the scale of the biological objects of interest (microns), constriction regions intended to hold such biological objects at user desired locations within the microfluidic devices during manipulation must be provided. These constriction regions are formed in prior microfluidic devices by means of traditional lithographic-based, microfabrication methods that involve etching. However, these traditional methods are inherently expensive due to the equipment, materials and process complexity issues required.
By way of example, Beebe et al., U.S. Pat. No. 6,193,647 discloses a microfluidic embryo handling device. The microfluidic device provided in the Beebe et al., '647 patent includes channels therethrough that incorporate various types of constriction regions for accurately positioning individual biological objects within the microfluidic device. The channels and the constriction regions formed therein are fabricated within the microfluidic device utilizing any suitable micromachining technique. The constriction regions may be formed by providing an obstruction in the bottom surface of the channel and sealing the channel of the microfluidic device with a cover. Alternatively, the sidewall portions of the channel of the microfluidic device may be constricted at a desired location to prevent passage of biological objects therethrough. In order for any microfluidic device to function properly, it is necessary that the constriction regions within the channels to be partially open such that the fluid carrying the biological objects may pass over the biological objects positioned at the constriction regions. In addition, it is preferred that each constriction region be sized so as to prevent the corresponding biological object from flowing therepast and to prevent an increase in pressure of the fluid used in the microfluidic device to move the biological object.
It can be appreciated that the shapes of the constrictions regions may take different forms, as long as, such shapes prevent passage of the biological object while simultaneously allowing fluid to flow through the constriction regions. However, these different forms of the constriction regions may require different manufacturing techniques. By way of example, “narrow” constriction regions within the channels of a microfluidic device are fabricated using a single mask and etching operation. Alternatively, shallow constriction regions within the channels of a microfluidic device are fabricated using two masks and two etching operations. Each of these masking and etching operations necessary to fabricate the constriction regions in the channels of a microfluidic device are complex and require specialized equipment. As such, the overall cost of manufacturing a microfluidic device can be significant.
As the use of microfluidic devices for bioproduction (e.g. protein production, assisted reproduction, etc. ) grows, it has become highly desirable to provide an inexpensive method of manufacturing various types of constriction regions within corresponding channels of a microfluidic device. If the manufacturing costs of microfluidic devices are reduced sufficiently, widespread use of microfluidic devices for such applications as incubation/maturation, infection, fertilization and/or chemical treatments of biological objects may become economically feasible.
Therefore, it is a primary object and feature of the present invention to provide a method of constructing a constriction region within a channel of a microfluidic device which is simple and inexpensive.
It is a further object and feature of the present invention to provide a method of constructing a constriction region within a channel of a microfluidic device which is capable to holding single cells or embryos at a known location within the microfluidic device.
It is a still further object and feature of the present invention to provide a method of constructing a constriction region within a channel of a microfluidic device which facilitates the speedy manufacture of such devices.
In accordance with the present invention, a method is disclosed for providing an obstruction in a channel of a microfluidic device. The channel has an input and an output for allowing the flow of fluid therethrough. The method includes the steps of providing a liquid mixture within the channel and solidifying the liquid mixture in the channel so as to form the obstruction.
The liquid mixture is a pre-polymer mixture and the step of solidifying the liquid mixture includes polymerizing the pre-polymer mixture. The liquid mixture is polymerized by being exposed to ultraviolet light. The ultraviolet light is generated with a source and is passed through an optical mask prior to polymerizing the pre-polymer mixture.
It is contemplated to add non-shrinkable material to the liquid mixture prior to solidifying the liquid mixture. The non-shrinkable material limits the shrinkage of the liquid mixture during solidification. In addition, the liquid mixture may also include a monomer, a cross-linking agent, and a photoinitiator.
In accordance with a further aspect of the present invention, a method is disclosed for providing an obstruction in a channel of a microfluidic device. A pre-polymer mixture is provided in the channel and exposed to a polymerizable stimulus such as an ultraviolet light from a source. The pre-polymer mixture shrinks and solidifies to form the obstruction in the channel.
It is contemplated to add non-shrinkable filler to the pre-polymer mixture prior to exposing the pre-polymer mixture to the ultraviolet source. The non-shrinkable filler modulates the shrinkage of the pre-polymer mixture. By way of example, the non-shrinkable filler may be glass beads. In order to expose the pre-polymer mixture to ultraviolet light, the ultraviolet light is generated by a source and passed through an optical mask. Thereafter, the pre-polymer mixture is exposed to the ultraviolet light. The pre-polymer mixture may include a monomer, a cross-linking agent and photoinitiator.
In accordance with a further aspect of the present invention, a method is provided for manufacturing a constriction region in a microfluidic device having a channel extending therethrough. The method includes the steps of introducing a liquid mixture including a monomer, cross-linking agent, and a photoinitiator into the channel. The liquid mixture is polymerized at a localized area within the channel so as to shrink the liquid material and provide an obstruction in the channel.
In order to polymerize the mixture, the liquid mixture is exposed to ultraviolet light. The ultraviolet light is generated with a source and passed through an optical mask. Non-shrinkable filler may be added to the liquid mixture prior to exposing the liquid mixture to the ultraviolet source. By adding non-shrinkable filler to the liquid mixture, the shrinkage of the liquid mixture is modulated such that the liquid mixture shrinks to a predetermined volumetric fraction of its original volume. By way of example, the non-shrinkable filler may be formed of glass beads.